Hα Filaments and Magnetogram
How can cool gas remain suspended for extended periods of time in the solar atmosphere?
Filaments tend to form along the boundaries between regions of positive and negative normal magnetic fields. Notice how the thin filaments seen on the Ha close-up image on the left tend to line up with the boundaries between regions of opposite polarities (pink-purple boundaries on the magnetograph close-up on the right); a fictitious line on the solar disk where the normal magnetic field component changes sign is called a magnetic neutral line. The fact that filaments are usually aligned with magnetic neutral lines strongly suggests that magnetic fields are responsible for supporting filaments (and prominences) against the gravitational field of the Sun.
Written By P. Charbonneau and O.R. White–April 18, 1995